Scrub typhus is a neglected infection long known to be endemic to the Asia-Pacific, where at least one million cases occur annually. New evidence indicates that the geographic range of and at-risk population for the disease are much larger. Scrub typhus has a mortality rate of up to 70%. The etiologic agent is Orientia tsutsugamushi (Ot), an obligate intracellular bacterium that invades leukocytes and endothelial cells. Despite its impact on global health, the bacterial factors that enable Ot to replicate in the cytosol without igniting the immune response and modulate host cell functions so it can proliferate are poorly understood. Ot encodes one of the largest armamentariums of ankyrin repeat-containing effectors (Anks) of any microbe and expresses all during infection. Thus, elucidating their functions is central to understanding Ot pathobiology. Most Ot Anks also carry an F-box motif, which facilitates ubiquitination of interacting proteins. We made exciting discoveries that three of these effectors (Ank1, Ank4, Ank6) modulate endoplasmic reticulum-associated degradation (ERAD) and the Nf-kB pathway. Ot is auxotrophic for amino acids and must parasitize them from host cells. The unfolded protein response is a cytoprotective pathway that relieves ER stress by promoting ERAD of misfolded proteins. Ank4 is linked to Ot?s ability to induce and benefit from ER stress. Aim 1 is built on the premise that Ank4 targets Bat3, a chaperone that is essential for ERAD, to modulate the degradative process to yield free amino acids that support the bacterium?s intracellular growth. In Aim 1, we will determine how Ot and Ank4 modulate Bat3 and ERAD to facilitate Ot proliferation in vitro and in vivo. Translocation of the transcriptional activator, Nf-kB, into the nucleus is the central initiating cellular event in the antimicrobial response. Aim 2 is driven by the premise that Ank1 and Ank6 contribute to Ot?s ability to block accumulation of Nf-kB in the nucleus and inhibit Nf-kB dependent transcription. In Aim 2, we will dissect how Ot, Ank1, and Ank6 modulate p65 to inhibit the Nf-kB response. We will fill a knowledge gap in the understanding of how a neglected pathogen of global biomedical significance establishes a permissive niche to replicate and cause disease. We will define new paradigms in the strategies by which intracellular microbes manipulate host cell functions, benefitting the microbial pathogenesis, cell biology, and innate immunity research communities. As ER stress and Nf-kB play roles in the development of other health disorders, including inflammation and cancer, this work will have an impact that extends beyond infectious disease.